The present invention relates to a flight guidance method of a high altitude unmanned aerial vehicle (UAV) for station keeping, and more particularly, to a flight guidance method of a high altitude UAV for station keeping in which a straight flight that connects points on the circle is used instead of a circle turning flight (loitering) so that fatigue of a remote pilot is reduced and the UAV is not lost due to a jet stream, etc. when the high altitude UAV automatically flies toward a destination of the stratosphere.
An unmanned aerial vehicle (UAV) is remotely controlled by ground control equipment, which is controlled by a remote pilot. Basically, the remote pilot controls altitude, velocity, and an azimuth of the UAV by manipulating dials (knobs). As a more automated method, the velocity and the altitude are controlled by the same method and the azimuth is controlled using a guidance method in which coordinates of a target destination are input by touch panel and the UAV is enabled to fly automatically to the destination. “Waypoint navigation” is representative of such a guidance method. A target point, which is coordinates of a target destination, is a specific point disposed on a plane irrespective of altitude.
Since the azimuth is frequently manipulated compared with the manipulation of the velocity and the altitude, waypoint navigation is a method that reduces fatigue of a remote pilot by automating the manipulation of the azimuth.
An automatic azimuth control method of waypoint navigation has two functions, one is a “destination guidance” function, also named LOS (line of sight), which fixes a target point and flies to the target point and the other is a “turning flight (loitering)” function, also named LOT (Loitering), which flies along a constant circle for station keeping when the target point is reached. Turning flight (LOT) is generally implemented in a circle shape. The automatic azimuth control method is a method in which, when a user moves the target point to a different point during turning flight, the UAV repeats turning flight after moving toward and reaching the different point.
Meanwhile, in the case of a high altitude UAV, because a wing span is large to enhance lift efficiency, a flight velocity is very slow at about 25 km/h and a rate of climb also very low at about 2 km/h. Because the UAV climbs very slowly, it takes a long time, such as about 6 hours, to reach a high altitude, such as the stratosphere of 12 km or more.
Further, in order to reach the stratosphere, the UAV passes through a section of a jet stream of 50˜100 km/h, and after reaching the stratosphere, and it is necessary to perform station keeping to maintain altitude and perform a work of long term endurance.
A flying object having a very low speed as described above may be wrecked due to fatigue failure of the flying object by being stressed when an appropriate corresponding action is absent to wind, may be blown by the wind and lost.
Further, since the UAV should fly within an approved flight area, the UAV having a low rate of climb reaches the boundary of the flight area in a state in which the UAV climbs a little altitude though climbing in straight flight, and here, the UAV should be turned.
As described above, the remote pilot becomes very tired due to 6 hours or more of individual manipulation corresponding to the flight area and the wind until the UAV reaches the target altitude.
Meanwhile, there is waypoint navigation, which is conventionally used as a method in which the UAV automatically climbs, flies and keeps station. However, waypoint navigation has a disadvantage. When using “destination guidance(LOS)” method in that case the pilot must input too many points considering with various wind condition. When using turning flight (LOT) method for station keeping, in that in the case of being turning flight (LOT) after reaching a target point, the target point is vague, and therefore the UAV may drift when wind is strong. That is, because a turning flight (LOT) method for station keeping, is implemented to follow the trajectory of a circle and is a method which decreases a distance between the location of the UAV and a normal line of the trajectory of the circle, so the target point does not exist on the trajectory of the circle. Therefore, when wind having a faster speed than the UAV blows, the UAV veers from the trajectory as a result of being pushed and drifts due to not having a particular target point.
Further, because the method described above needs constant turning flight, a control surface and an actuator are continuously loaded and there is a disadvantage in that energy consumption increases.